1. Field of the Invention
The present invention relates to a grout composition and, more particularly, to a pumpable, rehydratable grout composition for use in grouting conduits such as casing, tubing and the like in boreholes.
2. Description of the Background
Grouting or grout compositions are used in well and geotechnical industries for sealing and grouting well casings, plugging abandoned wells, and water-proofing earthen structures. In particular, in the completion of a well bore drilled into the earth, conduits, such as casing, tubing or the like, are normally lowered into the well and a cement slurry is pumped down the well and up the annulus between the pipe and the wall of the well bore. The cement slurry is then maintained in the annulus and allowed to set and bond to the pipe and to the wall of the well bore to thereby hold the pipe in place and prevent fluids from flowing behind the pipe. Numerous different cements and cement-type materials have been used for this purpose. For example, two commonly used grouting materials for grouting water wells are inorganic sodium silicates and organic polymers mixed with a cement slurry generally composed of Portland cement and water. It is also common in these grouting materials to employ bentonite and pozzolans as extenders.
Because of growing environmental concerns, water well cementing or grouting practices have been forced to change in the past few years. For example, grouting slurries containing organic polymers such as polyacrylamides and sulfonated polymers of some aromatic compounds used in prior art grouting compositions have become unacceptable for use in water well grouting in several states.
While there are non-organic-containing grouting compositions, they present several problems. For example, one common grouting method is to position dry, water-swellable clay pellets within the well bore annulus followed by the addition of water which swells the clay to thereby form an impervious layer in the annulus between the conduit and the well bore. However, this method of grouting has several disadvantages. For one, the clay pellets have to be placed in their intended location prior to complete hydration and often there are voids formed between the pellets. Accordingly, when water is added to swell the pellets, void spaces are left which create channels inside the grout column which will allow fluid flow between the conduit and the well bore.
Another common problem encountered in certain grouting compositions is shrinkage of the set grout. Such shrinkage leads to cracking of the set grout and is generally brought on by loss of moisture from the grout caused by differential formation pressure or formation temperature gradients. Since many of these prior art grouts contain generally water impervious or unswellable material added as fillers, once the grout is cracked, it is difficult, if not virtually impossible, to rehydrate. While this problem can be overcome by increasing the water-swellable clay content, this raises the viscosity of the grout composition to the point where pumping of the grout becomes quite difficult. Moreover, unless an effective dispersing agent is present, excess quantities of water-swellable clays, such as bentonite, result in the formation of "fish-eyes" which interfere with pumping.
Accordingly, a grouting composition which is useful in grouting of water wells and geotechnical wells, which contains no environmentally objectionable polymers, which can be disposed in the well annulus without the formation of voids and channels leading to fluid loss and which is readily pumpable and rehydratable, should cracking occur, is greatly needed.